Scrubbing CO₂ Cheaply

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The Siemens system uses a solvent made from amino acid salts instead. CO₂ can be removed and the solvent recovered by applying energy to break apart the chemical bonds formed between the two. This means simply boiling the solvent off, but the chemistry involved allows this to happen at lower temperatures. Amino acid salt formulations are also more stable than MEA and less likely to react with oxygen and sulphur dioxide in the exhaust gases; virtually none of the solvent should escape into the atmosphere along with residual gases. While the supply of other solvents needs to be regularly topped up because of these losses, this isn't the case with the amino acid salts, says Jockenhoevel. Instead of heating the solvent in one location to remove the CO₂, it is divided into two streams that are heated separately in a way that requires less energy.

Jim Watson, director of the Sussex Energy Group at the University of Sussex, in Brighton, U.K., cautions that the cost of carbon capture has to be balanced against the relatively low cost of buying carbon credits. He adds that developing the technology is expensive, and storing sequestered carbon reliably is an as yet unsolved problem.

However, Watson believes that the project is a positive step. "Anything that gets the efficiency losses down is important," he says. "The loss in efficiency is a very significant barrier to anyone taking up this technology."

Jockenhoevel suggests that the efficiency loss must be below 10 percent--any higher, and the cost of capture becomes more expensive for utility companies than paying for carbon-offsetting certificates, he says.

The technology will work with any kind of power plant that runs on fossil fuel and can be retrofitted to existing facilities, says Jockenhoevel. However, even if this summer's tests go according to plan, it will be years before the technology is deployed, partly because of the difficulty of storing CO₂, and partly because of the price of carbon on the carbon-exchange markets.

"It is low and very volatile," says Watson. Unless the cost of offsetting carbon increases, he says, carbon capture will remain a very pricey alternative.